Providing optimal service on the radio interface is an important aspect in mobile communication. In particular for packet-based traffic which has become more and more popular in the recent years due to the widely adopted Internet protocol as an example of a packet-based transmission protocol, optimizations for packet-based traffic consisting of data with varying quality requirements are demanded.
Certain applications, such as audio or video codecs, can be optimized by defining different quality classes for different bitfields, i.e. some fields are more important than others. Typically, protocol header fields (of all packets within a flow) require better protection than the data payload and are specifically protected, for example by using an extra cyclic redundancy check (CRC) code.
Another possibility is that different packets as such, within a packet flow, have different quality requirements based on the content of their payload section. However, until now no optimized and generic delivery mechanism in the packet domain has existed to take these differences into account.
In 2G and 3G cellular systems, this kind of support for different classes of quality of service is implemented for circuit-switched traffic.
Especially noteworthy is the GSM solution, where the most important bits are placed close to the training sequence midamble in a GSM burst, to get the maximum benefit from a good channel estimate. WCDMA supports radio bearer subflows, especially for use with adaptive multirate (AMR) speech audio codecs, for which every speech frame is split into three quality classes, which are then separately coded based on their quality requirements and optimally transmitted over the air interface.
A common characteristic for both, GSM and WCDMA approaches, is that the radio bearer subflows are configured statically prior to the transmission, either explicitly according to the specification, or by means of a radio bearer setup before the transmission starts.
For circuit-switched systems, the “radio bearer subflows” that receive different treatment on the physical layer, have to be pre-negotiated in the radio bearer setup.
Packet-based, i.e. packet-switched transmission differs significantly from circuit-switched transmission. Namely, in packet-based transmission, a flow might contain a stream of packets consisting entirely of a certain quality level, e.g. quality level 1 (Q1), with an occasional packet of different quality level, e.g. quality level 2 (Q2).
However, hitherto known scenarios cannot cope with such a situation. For the support of different quality classes of packets within a flow, a preceding setup signaling procedure to establish a radio bearer or radio bearer subflow for each targeted quality level is required. Furthermore, no packet-based solution for supporting different quality classes within an upper protocol layer packet is available in either GSM or WCDMA. In the circuit-switched solution the different subflows arrive separately to the radio link layer, and therefore no separation needs to be done by the radio link layer.